Urban stormwater runoff impacts Illinois waterways.
Stormwater runoff is rainfall and snowmelt that flows off hard, impervious surfaces such as roofs and parking lots and enters waterways through storm drains. As little as 10% impervious cover in a watershed can harm lakes and rivers. The more impervious cover there is in a landscape, the more stormwater runoff there is which causes a larger amount of fast moving water into streams, overwhelming them. This runoff can also carry pollutants, including phosphorus and nitrogen, into lakes and rivers.
- 1,262 miles of Illinois streams and 40,037 acres of lakes are impaired due to urban runoff and storm sewer impacts, according to the 2014 Illinois Integrated Water Quality Report
- Across six counties in northeastern Illinois, impervious coverage is estimated at 18%. This ranges from Chicago's Cook County at 50% impervious coverage, to suburban Will and McHenry counties, which are closer to 5% impervious coverage. Source: Illinois EPA Nonpoint Source Management Program
- The greatest source of phosphorus from urban stormwater is fallen leaves in the street are the greatest source of urban phosphorus according to a 2016 U.S. Geological Survey study. When it rains, phosphorus from the nutrient-rich leaves goes directly into storm drains and waterways.
Illinois urban stormwater ends up in the Mississippi River.
The NLRS Science Assessment determined that the amount of phosphorus and nitrogen leaving the state into the Mississippi River from urban stormwater is small compared to other sectors. However, urban stormwater is included as part of our state's nutrient effort because of its impact on our local Illinois waterways. The following statistics summarize baseline measurement information from 1980 to 1996. More information can be found in the 2015 Illinois Nutrient Loss Reduction Strategy Science Assessment Findings.
- Urban stormwater contributes 2% of the nitrate-nitrogen losses to the Mississippi River, which is 1.7 million pounds of the total estimate of 87.3 million pounds.
- For total phosphorus, urban stormwater contributes 4% of the losses to the Mississippi River, which is 0.72 million pounds of the total estimate of 18.1 million pounds.
Solutions for urban stormwater.
Only rain as it drains.
Urban stormwater practices, particularly green stormwater infrastructure, are important for the health of Illinois lakes and rivers. These nature-based solutions are strategically placed to intercept stormwater runoff and reduce pollutant loads. They can also prevent flooding, bolster climate resilience, enhance ecological health, and provide pollinator habitat. Examples include rain gardens, permeable pavement, and urban constructed wetlands.
Removing fall leaves from the street also reduces urban phosphorus loss. Many communities have a street sweeping program, which is an effective way to remove leaves and other sources of pollution. Together, these techniques can improve local water quality conditions.
Urban stormwater practices for communities.
Many Illinois communities implement stormwater management practices that benefit local and downstream water quality as part of their state-regulated Municipal Separate Storm Sewer System, MS4, permits. Extension staff conduct annual reviews of reports from nearly 300 of these permittees. This analysis shows that approximately 60% of MS4 communities report local ordinance requirements that support green stormwater infrastructure and nearly 70% of them sweep streets and collect leaves annually, thereby promoting water quality improvements. Additionally, many offer programs that raise awareness about clean water habits and incentivize installations of residential-scale green stormwater infrastructure practices.
Extension collaborates with local governments across Illinois to provide these programs:
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Written by Eliana Brown and Abby Bobrow
Post-production by Tucker Good and John Cambiazo